The present invention relates to innovative nanoparticles, to a process for preparing the nanoparticles by recrystallization, and to the use thereof.
Water-soluble compounds, namely molybdates, especially lithium molybdate, possess great interest as catalysts for accelerating the reaction of aqueous two-component polyurethane (“2K PU”) applications, since they contribute to accelerating the reaction without adversely affecting the pot life of the system.
Alkali metal molybdates are water-soluble, and so typically can be incorporated directly into the aqueous 2K PU formulations. Direct incorporation into a water-free component or composition, such as the isocyanate component, is not immediately possible in this way, since the alkali metal molybdates are normally in coarsely crystalline form and are insoluble or virtually so in the organic medium, thereby ruling out homogeneous incorporability. Moreover, the free NCO groups would react with the water of an aqueous molybdate solution, which is likewise unwanted.
It was an object of the present invention, therefore, to provide nanoparticles which can be formulated homogeneously in organic media in order to allow direct incorporation into water-free paint binders or crosslinkers.
This object has now been achieved by means of dispersible nanoparticles which have an average particle size of less than 500 nm. These particles are obtainable by means of a special preparation process.